This invention relates to a former for a bag maker and packaging machines incorporating such a former.
A bag maker-packaging machine, such as a vertical pillow-type form-fill-seal packaging machine as disclosed, for example, in U.S. Pat. No. 5,237,798 issued Aug. 24, 1993, makes use of a component commonly known as a former for bending an elongated flexible bag-making material into a cylindrical form, generally composed of a vertically extending tubular part and a so-called shoulder part (sometimes also called a skirt-like part) having a sloped planar guide section. The bag-making material, say, in the form of a web, is longitudinally transported towards the former horizontally in a flat form, moves over and along this sloped planar guide section of the shoulder part, changes the direction of its motion sharply as it crosses the connecting line at which the tubular and shoulder parts are attached together so as to move inside the tubular part and is pulled downward axially along the inner surface of the tubular part. In other words, the bag-making material is pushed upwards first over the sloped planar guide section of the shoulder part, changes the direction of its motion sharply at the connecting line as it is folded into a tubular form, and then is pulled downward by the force not only of the articles which are dropped in to be packaged in the bag being made but also of a pull-down belt or the like (not shown) for causing the motion of the bag-making material. Thus, it is crucial that the connecting line, at which the bag-making material is forced to change the direction of its motion sharply, be a continuous smooth curve shaped correctly because, if it is not shaped correctly or has even a small unevenness, the material is likely to become wrinkled or develop small longitudinal lines on the surface.
Formers of this type are usually produced by casting, a master mold being used thereafter to carry out an accurate copy process for shaping the connecting line correctly. This, however, requires a long time of hard work by an experienced worker, adding to the production cost, and fluctuations and non-uniformity in the shape of formers make them non-exchangeable. Moreover, many formers are usually required for producing bags of different sizes. Even when bags of the same size are produced, different formers are generally required, depending upon where and how the side edges of the elongated bag-making material should be overlapped for longitudinal sealing. The angle of the sloped planar guide section of the shoulder part must be changed, furthermore, depending on the physical properties of the bag-making material such as its thickness. In short, the cost of equipping a bag maker with a sufficient number of formers with different kinds is substantial if prior art technology is relied upon.
It is therefore an object of this invention to provide a method of producing formers of different kinds accurately and automatically.
It is another object of this invention to provide formers produced by such a method, having their tubular and shoulder parts formed by bending pieces which are cut from a blank sheet by a numerically controlled cutting machine.
A former according to the present invention, with which the above and other objects can be accomplished, may be characterized not only as being composed of a hollow cylindrical tubular part defining an axial direction and a shoulder part which has a planar guide section and is attached to the tubular part along a closed three-dimensional line (referred to as the connecting line) such that an elongated bag-making material transported over the sloped planar guide section of the shoulder part can be made into a tubular form as it crosses the connecting line to move into the tubular part, but wherein the aforementioned connecting line between the tubular and shoulder parts is shaped such that the angle between its tangent and a plane perpendicular to the axial direction of the tubular part changes at a constant rate with respect to the change in position of the contact point of the tangent with the connecting line, for example, in the direction perpendicular to the axial direction of the tubular part or along the connecting line itself.
To produce such a former according to the present invention, pieces to be made into the tubular and shoulder parts are cut out from a blank sheet in specified geometrical shapes, bent and folded appropriately into predetermined shapes of the tubular and shoulder parts, and attached together, say, by welding, along the aforementioned connecting line. The geometrical shapes into which the blank sheet is cut are determined such that, when these pieces are bent, folded and attached together as described above, the connecting line therebetween will satisfy the condition imposed according to this invention as described above regarding the rate of change in its slope.
Depending upon what kind of seals are desired, side strips of different widths may be provided along the side edges of the pieces to be cut out from the blank sheet.